Monthly Archives: May 2014

What You Need To Know to Become a Penetration Tester

It really has been a long time since I last posted. This post is more of an essay, so it may be a TL;DR for some, but hopefully a there is some good information for those who wish to break into Penetration testing or at the very least something I can point people to next time I’m, asked.


As I’m sure is the experience of other Penetration Testers, I’m often asked (or see slapped across LinkedIn Forums) by a whole range of people “How do I break into Penetration testing?” or the like. The prospect of becoming a ‘professional hacker’ is all too enticing for graduates, IT professionals and even Information Security bods in other functional areas alike. Having answered this question and posed many a question in rebuttal, I decided to formalise my experiences, musings and advice into a single blog post. I hope it helps.


What is Penetration Testing?


To begin with, it’s always worth checking your understanding of what a Penetration tester actually is, does and some of the attributes belonging to the ‘good and great ones’. Being a Penetration tester is not the same as being (what the media often portray as) a hacker. To dispel a couple of myths about Penetration testing, it’s worth describing some of the aspects of the job in bullet points for brevity.

  • For most of the industry, a Penetration test does not involve development of 0-day exploits.
  • Normally, you get a very limited amount of time (days) to compromise systems that hackers would have months to do.
  • You always have to document your findings in a written report at the end of the test. Often, you will be asked to explain in detail some or all the findings to technical and non-technical audiences.
  • In a lot of cases, clients aren’t looking for a single route to domain admin. They’re interested in their broader attack surface and coverage across their whole estate.
  • Business considerations, such as loss of earnings due to downtime and cost of engagement are much more important than you may initially think (or probably not consider at all before testing).


What makes a good tester?


I believe that there are quite a few considerations beyond raw technical knowledge that make a good tester. It’s key to remember again that Penetration testing is not ‘hacking’ and although there is a place for the borderline-autistic who hacks the Pentagon on their neighbours’ wireless, it’s more likely they’ll be suited to research or the Russian mafia. Again, I’ve added a bullet pointed list to describe some of what I consider key attributes of good and great testers that I consider when I hire non-experienced testers.


  • The right attitude – This is much more important than someone who’s done a course (CEH or the like). The truth is, I don’t believe that you can be a good Penetration tester if you’re not passionate about IT Security and moreover technology. It does need to be more than a job, as the up-skilling and constant personal development is not possible to maintain if your heart’s not in it. Also, you need to be fairly autodidactic (into self-learning) as even now there are few good core texts on most topics and they become outdated quickly. Most experienced tester will have gone through a huge amount of self-learning and will be resentful if you expect it on a plate (others just plain don’t want to share).
  • Good fundamentals – The best testers know a lot about a few things, but something about everything else. Despite some academiphobia (is that a word?) within the industry, I think that an IT related degree provides a great grounding in computer science and will stand you in good stead. Similarly, experienced sysadmins, network architects and developers should have good foundations on which to build. It’s common to find testers with big knowledge gaps, it’s really important to understand all areas of enterprise infrastructure to some degree in order to progress through the ranks.
  • Technical Prowess – At its core, Penetration testing is an extremely technical discipline. Not only do you need to understand how things work at a low level, you need to subvert controls in a repeatable way and learn constantly as new versions of software/hardware are released. The ability to code or script is always an advantage, even if you’re limited to simple bash scripting. However, some of the best testers I know can’t write code but can read and break very well indeed. That said, it will limit your vision and scope ultimately if you can’t. More on this later!
  • Soft and Written skills – Often overlooked, these skills are what separates Penetration testers from hackers and script kiddies. Ask yourself, would you as a client accept the work of someone who cannot write a coherent sentence, who cannot express simple issues in plain English and pay over £1000 per day for the pleasure? The key deliverable for the client is the written Report. Penetration testing companies require consultants who can read, write and speak English well. Unless you’re a total genius who’s finding 0-days nobody else can, they’re unlikely to overlook total ineptitude in this area.


Where to Start


In general, I would say that it’s almost impossible to get into a Penetration testing job at any level if you lack any exposure to computer science or hacking. It’s not like sales where you can start at the bottom with nothing and there are thousands of jobs.

From my experience, there are four common starting points that lead people to the Penetration testing path. Apologies if this doesn’t fit your circumstances or I’ve left out anything that’s obvious.

  1. A school or college leaver who hacks as a hobby.
  2. An existing IT professional (e.g. Sys admin, Developer, Network Engineer)
  3. A recent graduate of Computer Science, Cyber Security or Ethical Hacking
  4. A graduate or experienced professional in another field

Scenario 1

In Penetration testing, having a lack of schooling and higher / further education isn’t necessarily a hindrance if you have some skill. However, you will likely need to prove this to a greater extent than perhaps a graduate would. Bug bounties are a great way to prove your prowess, with sites such asBugcrowd paying sizeable winnings to the best bug hunters. If this is beyond your current skill level, it’s worth playing with some of the teaching frameworks such as Metasploit Unleashed or DVWA to hone your skill. It’s worth remembering that companies pay large amounts of money to recruiters, so if you approach them directly with a well-written CV, they’re likely to appreciate your enterprising spirit as well as the potential cost savings! If your CV is short or particularly unimpressive, you should pay particular attention to writing a covering letter or email. This should be well constructed and demonstrate your keenness to work for that company specifically (everyone likes a bit of mild flattery) and a bit about your background and aspirations. It’s worth noting that most (me included) organisations will throw out emails or CVs that are poorly written or full of mistakes at first sift. If you’re not grammatically gifted, ask someone who is to assist.


Scenario 2

Existing IT professionals already have quite a bit of skill (potentially) in a useful area. This is often quite attractive for Penetration testing companies as they understand general working practices and professionalism (one would hope!) and are often very keen! My advice would be to avoid expensive courses and retraining in order to land a job, but to focus on moving into a role as quickly as possible. There are plenty of cheap or free resources online to gain some basic knowledge around testing to move up to a level whereby you can hold a decent conversation in an interview or demonstrate working knowledge of Metasploit or Burpsuite on a rig. I always believe that attitude is more important than current skill-level with inexperienced hires, and spending £3k on a SANS course won’t make you start any higher in an organisation without testing experience. Great resources for this type of up-skill can be found on sites like SecurityTubeUdemyOWASP (or just YouTube) and courses like Metasploit Unleashed and Mutilidae will help you reach initial goals.


Scenario 3

As a recent graduate, you have likely been exposed to good basics across a wide breadth of IT; some of it you may even remember. For those of you who have done a Computer Science degree and particularly enjoyed a security module or completed a Security or hacking related dissertation, you may feel the next step is to apply for a Penetration testing job. In this scenario, my advice would be to make totally sure it’s what you want to do and commit. As an interviewer, I’m always looking for a passion for security and some evidence of learning outside of University in this field, or as a minimum, a good security-focused FYP. If you’re lacking this, it will likely seem as though you don’t know what you want to do and you saw a couple of jobs being advertised for senior Penetration testers for up to £100k. For the people who’ve done a Security-related degree (or Masters) at Universities such as Abertay, Glamorgan, Kingston, Royal Holloway etc. you’re likely to get to the interview stage based on the specificity of your experience (as long as you got a reasonable grade).


Scenario 4

If you’ve no experience or qualifications in the field, then it’s likely to be a struggle to get an interview on the strength of your CV alone. I would advise the same approach as a School or College leaver, get ethically hacking and learning! An impassioned covering letter and interest in being an unpaid intern will often turn the heads of a hiring manager.


Industry Accreditation


This is probably the most frequent area of questioning I get when people ask me about moving into the industry. As the industry is so heavily focused on the CESG CHECK scheme, it’s best to separate the discussion into two parts, the CHECK scheme and other qualifications.




The CHECK scheme was initially set-up in response to the increased demand for skilled Penetration testing to be performed against HMG (Her Majesty’s Government) assets and CNI(Critical National Infrastructure) in the form of ITHC (IT Health Checks). In short, the Government didn’t have the funding to hire enough heads internally to complete all the work at the right level (or the salaries to tempt good testers away from industry). Therefore, the CHECK scheme was created as a framework to manage the subcontracting of this extra effort. A large amount of Penetration testing firms rely heavily on work from the CHECK scheme and it remains a huge source of income. Both companies and individuals can accredit to the scheme, with approved organisations deemed as ‘Green light’ should they satisfy the required criteria.


The accreditation of individuals is quite complex, and even experienced testers still sometimes get confused by the different options. There are essentially two grades of Penetration tester within the scheme, CTL (CHECK team leader) and CTM (CHECK team member) with the former being the top tier. In order to achieve either of these levels the individual must pass an exam, hold SC clearance and work for a CHECK green light company. SC clearance can be attained by UK and Foreign nationals’ resident within the UK. However, if you’re not a British citizen you will often be caveated with ‘UK eyes only’ on your clearance, which will stop you from doing certain types of work. At the time of writing, the following table shows the possible examination paths to accreditation.


CHECK Team Leader
CHECK Team Leader (Infrastructure) CREST Infrastructure Certification Examination (
Tiger Scheme Senior Security Tester (
Cyber Scheme Team Leader Examination (
CHECK Team Leader (Web applications) CREST Certified Web Application Tester (
Tiger Scheme Web Application Tester (
CHECK Team Member
CHECK Team Member CREST Registered Tester Examination (
Tiger Scheme Qualified Security Tester Examination (
Cyber Scheme Team Member Examination (

Fig.1 – Taken from CESG website


The main difference between a CTL and a CTM (apart from the difficulty of the exams) is that a CTL must author the report and lead the testing. A CTM cannot work solo on a CHECK test. Therefore, a CTL is more valuable to a company that performs CHECK work as they can work alone, which makes scheduling more easy and it’s likely the tester is more highly utilised. The CTL grade subdivides into Web Applications and Infrastructure, however, there is currently no restriction on what type of work a CTL can perform either on their own or with other testers (i.e. a Web Application CTL can perform Infrastructure work solo).

Most testers will aspire to pass these exams, certainly when working within a CHECK Green light organisation, as their employer will either mandate or encourage it. The CTL exams are all-day and quite challenging, even for experienced testers. More information on the specifics of the exams can be found on the sites listed in the table above.


Other Industry Accreditations


There are loads of courses and accreditations out there, I have just listed and given a few lines about the courses and my opinions on each in order to give a flavour of the common ones.


CEH – The general consensus of testers in my experience is that CEH lacks technical detail and isn’t really a very good qualification for a Penetration Tester. However, I have not completed this exam myself and base my opinions on the experiences of trusted colleagues and the course syllabus and examination guides. I wouldn’t recommend this certification if you wish to be a Penetration tester.


OSCP / PWK by Offensive Security – This is a pretty technical course, which many of my team and colleagues have done. The course uses Kali Linux as a base operating system and runs you through a challenging series of labs exploring scripting in bash and python, the basics of exploit development and loads more. It’s online and give you VPN access to the various labs required for the course. In order to gain the OSCP qualification, you are required to submit coursework from the labs and complete a challenging exam over the course of 24hrs. Feedback on this has always been that it’s awesome and very challenging.


SANS Courses – Again, I have never been on a SANS course, but I have seen a lot of the material (having put some of my team through these), know a few instructors and have heard good things across the board. My one criticism is that most of the exams are multiple choice and not practical-based, which is a bit disappointing. That said, the instructors of the on-site courses are always excellent and if you can keep up you’ll learn a lot. I believe that it is more of a standard in the US to go after the GWAPT or GPEN exams.


BEWARE recruiters


I decided not to do a section on CVs, as I felt it was a bit patronising. Suffice to say, don’t send your CV across with any mistakes (spelling, grammar or otherwise), don’t leave any unexplained gaps and don’t in clude huge sections on your non-security related hobbies.

I supposed that finding a job often starts with recruiters, or at least LinkedIn. I have a hard time working out which is which nowadays, but it’s where I shall begin. For a lot of companies, recruiters are a necessary evil, but it’s best to attempt to avoid going through one unless it’s a necessity (some larger companies may mandate this route).


I have literally hundreds of horror stories about recruiters in Penetration testing, which I won’t bore you with, but be wary of sending them your CV (and moreover them getting hold of your CV, sending it to loads of companies then ringing you to see if you’re interested in any that bite). I would advise that you take their advice with a pinch of salt as most don’t understand the market. You can waste a lot of time being sent to far-flung places for inappropriate jobs that a recruiter persuaded you was a good idea (in order to make their quote of candidates to interviews). If you’re unsure, don’t be afraid to ask to speak to the company on the phone first to clarify the role is suitable.


I would advise that you approach reputable companies directly, you can find a list of CHECK Green light companies here for reference.


If you’re following my advice and taking a direct approach, I would always advise that you check the company website first to see if they mention hiring on there. As I mentioned earlier, most organisations will see it as a positive thing if you track down the right person (or at least an appropriate one) on LinkedIn, send them a bespoke email introducing yourself and asking them about hiring and if they’d consider you for an interview. This saves them money, and shows a bit of initiative on your part.


The Interview Process


Most interviews I’ve done (as an interviewee and interviewer) for testing roles have all followed a fairly formulaic approach. They usually follow a two or three stage process with a mix of the following aspects:

  • Phone-based – Some simple technical questions (Nmap flags, Port numbers, What’s a XSS? etc.) and to check you speak good English and have a brain.
  • Face-to-face (Technical) – This normally is a series of technical questions and a technical assessment on a rig of some kind, often with you explaining as you go or the interviewer(s) watching on another screen what you do. This can be very intimidating as they tend to bring in very senior technical people to watch. Normally this will be pretty basic like popping a box with MSF (using MS08-067) or basic XSS.
  • Face-to-face (Presenting / meet-the-director) – You may be asked to present a Penetration test report or prepare something to assess your interpersonal skills. Depending on the company, you may need to meet a higher level business representative such as a director or partner.
  • Face-to-face (General) – A general interview will have a mix of discovery questions, often using HR methodologies such as the STAR model. This type of interview will seek to find out a bit more about you as a person and your aspirations to check for a cultural fit.


Before you go to the interview, it’s always worth asking what will be required and if you need to prepare anything. Interviews are an opportunity to sell yourself, mention anything related to the field of penetration testing that you have done. I recall one specific interview with a very shy gentleman, he really struggled explaining to me some really basic concepts such as what port scanning was and had never heard of the OWASP top 10; things were taking a nose-dive. Suffice to say, he hadn’t done well and didn’t appear to have a clue about anything in security, after having quite a promising CV. At least until I asked him the question ‘what do you do in your spare time?’, to which he answered “oh, I like exploit development and malware reversing normally, you know that bug that was found in IE last week, that was me, I got £10k from Microsoft for that”. Totally mental that he didn’t mention that, even after I asked him the ubiquitous ‘tell me about yourself?’ at the start of the interview.



I hope that my post has provided a useful amount of information to aspiring Penetration testers, if you have any comments, criticisms or more questions please leave them below.

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